Television receiver



Dec. 23, 1941. F. OKOLICSANYI TELEVISION RECEIVER 2 Sheets-Sheet 1 l4fly? FQfQuQ (DKoHQSanJI I Filed Jan. 19, 1939 Dec. 23, 1941. F.OKOLICSANYI TELEVISION RECEIVER Filed Jan. 19, 1939 2 Sheets-Sheet 2Patented Dec. 23, 1941 TELEVISION RECEIVER Ferene Okolicaanyi,Kensington, London, England Application January 19, 1939, Serial No.251,844 In Great Britain January 21, 1938 9 Claims.

The present invention relates to television receiving apparatus using asupersonic light control device, that is a device in which modulatedmechanical waves of supersonic frequency are generated in a body or onits surface and are used to modulate a light beam falling on the body inaccordance with the modulations of the waves.

Such a device is described in British Patent specification No. 439,236.In one method of using such a device a train of waves is produced in thecell by a piezo-electric crystal set into oscillation by a highfrequency electrical oscillation modulated in accordance with thereceived picture signals. The train of waves therefore represents in itsamplitude the brightnesses of a number of successive picture points; animage of this train of waves, which modulate the light passing throughthem in accordance with their amplitude is formed on the screen andmoved over it at such a speed that the movement of the waves themselvesis immobilised on the screen, that is each picture point is reproducedon one spot on the screen so long as the corresponding modulations inthe cell are present therein. In such a method the waves in the cellmove in the line scanning direction.

It has been proposed to construct a television receiver by placing sideby side a number of Kerr cells. and to cause these cells to operate oneafter the other by applying a Potential to their plates from a cathoderay beam of which moves over a number of contacts arranged within acathode ray tube, each contact being connected to one of the Kerr cells.In this way there is produced a beam of light having a scanning motionalong the line of cells and if the intensity of the cathode ray beam ismodulated with received picture signals, the moving light beam willtrace out on a screen on to which it is projected, a picture line havingas many elemental areas in it as there are Kerr cells.

It is an object of the present invention to improve on a device of thiskind so that the disadvantages inherent in the Kerr cell type of lightmodulator are removed.

It is a further object of the present invention to provide a televisionreceiver in which the light is modulated by a number of wave trains ofhigh frequency mechanical waves moving parallel to one another, the wavetrains being produced by a number of vibrating bodies which are set intooscillation in turn by means of a cathode ray commutator.

As a further object-the present invention proposes to employ in place ofa series of Kerr cells.

a cell employing high frequency mechanical waves for light modulation,and to construct the cell in such a manner that a series of wave trainsmoving at right angles to the line scanning direction of the apparatus,each wave train being modulated in accordance with the brightness of oneelement of the reproduced picture, are produced by a cathode ray beammodulated in accordance with the received picture signals.

Various embodiments of the inv ntion or parts thereof are shown in theaccompan ng drawings of which Fig. 1 shows diagrammatically the opticalsystem and the light modulating device of a receiver according to theinvention,

Fig. 2 shows a cathode ray commutating device for use with the apparatusof Fig. 1,

Fig. 3 shows an alternative method of eifecting cooperation with thecommutating device and the light modulating device,

Fig. 4 shows an alternative form of cathode ray tube,

Figs. 5 and 6 show in end view and plan view a part of Fig. 4.

Figs. '7 and 8 show in detail alternative constructions of the lightmodulating device. Referring to Fig. 1 of the drawings, a televisionreceiver embodying the present invention comprises a lamp I, having along incandescent filament 2. Light from the filament is collected by alens 3 and projected on to one transparent wall of a composite lightmodulator cell 4. The upper wall of this cell 4 is composed of a steelplate adjacent the liquid and having fixed on its upper surface a numberof piezo electric crystals arranged side by side along the length of thecell (that is in a direction parallel to the filament 2) and each beingprovided on its upper surface with a second electrode. These secondelectrodes are shown at 5. In the drawings fifteen of such electrodesare shown, but in practice the cell would be provided with as manycrystals as elemental areas it is desired to reproduce in a line of thereceived picture. The transparent side walls of the cell 4 through whichthe light passes are provided with cylindrical lenses la. and lb havingpower in the plane of the wi ith of the cell 4. Beyond the cell 4 is anopaque bar 6 and a mirror oscillograph I of the Rochelle salt type anddesigned to provide the low speed scanning component, and to projectlight from the cell 4 on to a screen.

Between the oscillograph l and the screen 8 are provided two cylindricallenses 9 and III, the lens 9 having power in the plane containing thelength I of the cell l and the lens in having power in the plane of thewidth of the cell 4. The function of these lenses will be describedhereinafter.

The crystals of the cell 4 are set into oscillation by means of acathode ray communication shown in Fig. 2. In that figure, a cathode raytube comprises a straight filamentary cathode H and an astigmaticelectron lens system shownby way of example in the form of two slotteddiaphragms l2 and I3 so positionedand in operation given such voltagesthat a line electron image of the cathode II is formed on a contactassembly I I4. Deflector plates l5 and [6 are provided for deflectingthe beam over the contact'assembly |2.. The cathode II is surrounded bya wehnelt cylinder ll having a slit-shaped aperture Ila to act as amodulating electrode for the cathodev beam.

The contact assembly [4 comprises as many contacts l8 as there arecrystals on the cell 4,

, line is being generated.

which extends the whole width of the received picture).

Any suitable form of low speed scanner-may be used, such as a mirrordrum, in place of the oscillograph mirror I. The present inventionhowever permits the use oi such small scanning elements owing to thefact that it is-not'necessary to focus an image of the cell in itslonger dimension as in thecase oi the cell described in British Patentspecification No. 439,236, thus giving freedom of focussing in thisdimension.

It is possible to make the-width of the cell 4 (that is the dimension inthe direction of movement of the waves) sufliciently large so that onetrain of waves is still moving through the cell while a second traincorresponding to the next This can be done by 1 choosing a liquid mediumin which the waves mounted on an insulating member lll which istravelslowly, for example ethyl iodide. In this case the slow speed scanner .1can be arranged tomove at such a speed thatithe images of the wavesformed on the screen 8 are always projected on the same spot thereon,that is to say th'emovement or the waves in the cell is immogeneratingsupersonic mechanical waves in the.

liquid of the cell 4 of Fig. 1 is modulated with the received picturesignals and applied to the modulator electrode ll of the gun of thecathode ray tube of Fig. 2. The line synchronising impulses are used togenerate a'saw tooth oscillation which is used to deflect the beam overthe contact assembly M at line frequency. For this purpose the normaltelevision receiving circuits may be employed, such are illustrated inFig. 4 and described later in this specification.

As the beam moves over the contacts I 8, an oscillating potential willbe applied across each of the crystals of the cell 4 in turn for a shorttime, and each crystal will set up in the liquid of the cell a shorttrain of waves, which will travel from the crystal surface downwards asthe cell is shown in Fig. 1. Each train of waves willdifiract part ofthe light passing through it, th'e amount of light difiracted beingdependent upon the amplltude of the waves. The undififracted light isarrested by the opaque bar 6, and the diffracted light passes on to thelow speed scanner 1, and thence to the receiving screen 8.

The optical system consists of a number of cylindrical lenses, eachhaving power in oneof two mutually perpendicular planes, and thereforethe focussing in each plane can be considered separately. In the planeparallel to the direction of movement of the supersonic waves the lenses4a, 4b and Ill have power. The light from the filament light source 2 isrendered parallel by the lens 4a, and brought to a focus on the bar 6 bylens 42;. The lens Ill forms an image of a plane near the bar 6 on thescreen 8. In the plane at right angles to this, the lens 3 acts as acondensing lens to throw light on to the cell 4: the

lens 9 forms an image of the cell 4 on the screen 5. The distances ofthe lenses 8 and in from the cell i and bar 6 are arranged to be suchthat the image on the screen is narrow (i. e. the lens W forms a reducedimage of th'e light passing the bar, and the lens 9 forms an image ofthe cell thepicture may be projected bilised on the screen. Thus, two ormore lines of on the screen simultaneously.

Instead of having the cathode ray beam commutator at a point remote fromthe cell as shown in Figs. 1 and 2, with wire'connections between thecontacts of the commutator and the crystal electrodes, the cathode raybeam may be ar- 7 ranged to fall directly on the electrodes 5 of thecrystals by constructing the end wall 01 the tube as the cell itself. Apreferred construction is shown in Fig. 3. I

In this flgure, the end of a cathode ray tube, part'of the walls ofwhich are shown at 24, has sealed into it a plate 25 or ceramicmaterial, the centre part of which 26, is made very thin. On the side ofthe part 28 are fixed a number of contacts 21 on to which the cathoderay beam, indicated by the dotted line 28, falls. On the outer side ofthe plate 25 is attached the light modulating device 29. The end of thisis closed by a thin steel plate 30, on to the outer side of which areattached a number of piezo-electric crystals 3i, each of which isprovided with a second electrode 32, these second electrodes lyingopposite the contacts 21 on the opposite side of the plate 25. Betweenthe contacts 21 is a layer of resistive material connected to earth insuch a manner that there is a resistive electrical path between eachcontact and earth. When the beam falls on a contact 21, the potential ofthe latter varies according to the modulation of the beam, and acorresponding voltage is set up across the crystal between the electrode32 and the plate 30, due to the capacitive connection between thecontact 21 and the electrode 31. The V vibration of the crystal sets uphigh frequency waves in the liquid of the cell 29, which waves are usedto modulatea light beam and to reproduce th'e received picture in themanner described with reference to Fig. 1.

In the case where it is desired to produce a larger picture on thescreen, the cell 4 of Fig. 1 must be made large in order that sufficientlight may be present in the system to illuminate with a reasonablebright intensity a large screen. The crystals must then be alsocomparatively large, and in practice a simple cathode ray tube of thetype shown in Fig. 2 may not give the power required to set the crystalsinto oscillation with suiiicient amplitude. In Fig. 4 is shown anelectrode arrangement for a cathode ray commutator in which a largerpower than that given by the arrangement of Fig. 2 can be obtained.

In Fig. 4, a cathode ray tube has a first cathode 35 which is in theform of a short filament running at right angles to the plane ofthepaper. This cathode is heated by current from a battery 36. Next to thecathode 35 Ba modulating grid 31 and then a magnetic focusing coil 38,which is designed to project a line image of the cathode on the grid 39,in close proximity to which is placed a collecting electrode 34. Thearrangement and function of this part of the apparatus will be describedmore fully later. A pair of defleeting plates 40, 4i, are provided fordeflecting the electron beam from the cathode 35 over the grid 39. Asecond cathode 42 is arranged on the side of the grid 39 nearest thecathode 35, and to one side of the path of the electrons from the firstcathode 35, so that these electrons pass it, and fall on one side of thegrid 39. The cathode 42 is heated by a battery 45. On the side of thegrid 39 remote from the cathodes is placed a modulating grid 43, then amagnetic focusing coil 44, and finally a contact assembly 45, thecontacts on which may be connected by wires to the electrodes of thecell, as described with reference to Figs. 1 and 2, or may be attachedto the cell as described with reference to Fig. 3.

The construction of the grid 39 and the relative positions of this grid,the electrode 34,and the cathode 42 are shown in Figs. 5 and 6. The grid39 comprises two supporting uprights 56 and 51, the upright 51 beingmade of, or being coated with a layer of resistive material. Theconnection to the outside of the tube is made by a metal conductingstrip 58. The grid consists of a number of small grids 59 arranged sideby side spaced apart from one another, and connected to the resistiveelement 51. The number of grids 59 is made equal to the number ofelements it is desired to reproduce in a picture line, that is equal tothe number of crystals of the modulating cell 4 of Fig. 1. The positionof the cathode 42 relative to the grid 39 is shown in dotted lines inFig. 5, and as a full line in Fig. 6, and the beam from the cathode 35falls on the grids 59 on that part of them which is between the cathode42 and the support 56. The electrode 34 consists of two plates (whichare suitably connected together electrically) arranged one on each sideof the beam from the cathode 35, and held at a high potential relativeto the grid 39, which is biassed negatively relatively to the cathode42. The connections of these electrodes to the battery 55 are shown inFig. 4.- Preferably a shielding electrode 69 connected to the cathode 42is provided between the latter and the collecting elecgrid 31, which isbiassed negatively with respect to the cathode 35 by connecting it tothe negative terminal of a source of voltage 55, and connecting thecentre tapping of the battery 35 to a more positive tappin on the source55. In this way the beam falling on the grid 39 will be modulated withthe received picture signals.

Now when the beam falls on one of the grids 59, this grid emitssecondary electrons, and it is arranged by suitably choosing thepotential difference between the cathode 35 and grid 39, and by makingthat part of the grid 59 of suitable material (e. g. by coating it witha substance which readily emits secondary electrons) that the number ofsecondary electrons emitted exceeds the incident electrons. There willbe produced on the grid 59 in question a positive charge proportional tothe strength of the beam falling thereon, which is in turn proportionalto the brightness of the corresponding picture element. The resultingdecrease in negative. bias of the grid 59 will result in a fiow ofelectrons from the cathode 42 through the grid 59. This electron currentpasses through the grid 43 (Fig. 4) on which is impressed a highfrequency oscillation of the frequency required for driving the crystalsof the light modulating device. This frequency is generated by anoscillator 6! and fed to the grid 43 through a transformer 62. Thefocussing coil focusses an electron image of the grid 39 on to thecontact assembly 45, the image of each grid 59 in the grid 39 beingimaged on one contact. Thus each contact will have falling on it a beamof electrons which is modulated in amplitude by the picture signalcorresponding to it and by the high frequency oscillation from thegenerator GI. and a corresponding train of waves will be set up in thecell and used as described with reference to Fig. 1. When the beam fromthe cathode 35 moves ofi one grid 59 on to the next one, the charge onthe first grid will begin to leak away through the resistive support 51,the resistance being such that the charge received from the beam fromthe cathode 35 has substantially entirely leaked away within' one lineperiod. It will be seen that'the above apparatus provides a certainstorage effect, since a modulated oscillation continues to be applied toeach contact after the beam has moved away from the corresponding grid,due to the time required for the charge to leak away. from the grid.

It has been observed that if a quartz piezoelectric crystal has only apart of its surface covered with the electrodes, and an oscillation isapplied thereto, only the part of the crystal covered with theelectrodes will vibrate, the retrode 34. The bias on the grid 39 is suchthat no emission from the cathode 42 passes it.

The operation of the cathode ray tube is as follows. Television signalsreceived by the aerial 41 are amplified by an amplifier 49, and appliedto a separating arrangement 49 which separates the picture signals, linesynchronising signals and frame synchronising signals from each other.The frame synchronising signals appear at 59 and are used to control theslow speed scanner 1 of Fig. 1. The line synchronising signals appearingat 5| are fed to a time base circuit 52 to control the generation of sawtooth impulses at line frequency which are fed to the deflecting plates40, 4|. The picture signals appear at 53 and are fed through a condenser54 to the modulating mainder being unaffected.

The present invention therefore provides a modification of thearrangements previously described, in which the crystal assembly isreplaced by a single crystal extending over the whole length of thecell. In one example, illustrated in Fig. 'l, the crystal 8B is coveredon the side remote from the liquid by a number of separate electrodes8|. These electrodes may be formed of fine wires, and the spaces betweenthem may be filled with an insulating material. On the other side of thecrystal is fixed a common electrode 92, for example a steel plate.

In an alternative arrangement using the above stated fact, the crystalsurface is itself exposed to the cathode ray beam in place of thecapacity connection shown in Fig. 3. In this case the focussing systemof the tube, which may be a cylindrical focussing system, preferablycauses the beam to fall on a narrow strip of the crystal taken at rightangles to the longer dimension of the latter.

In any of the embodiments of the invention described above, the distancebetween the crystal or crystals and the opposite wall of the cell can bemade such that the wave reflected from this wall produces standing waveswith the waves from the crystal. By utilising the reflection of thewaves to and fro across the cell, the effect of the waves may be made topersist for some time after the scanning cathode 'ray beam has passed onto another part of the crystal or crystal assembly, thereby giving anenhancement-of the light passing through to the screen.

The cell wall may be fitted with a special refiecting surface as shownin Fig. 8. The reflector can be made from, for example, a polished planemetal surface 83, which may be of stainless steel. The distance of thereflector from the crystals 84 is made very short to achieve a multiplereflection. In this way, the short excitation of the supersonic waves inthe liquid is prolonged for the whole duration time of a line. It isalso an advantage to apply only a low damping to the crystal to obtainin this way a persistance of the oscillations, for example by excitingit with a frequency which is a harmonic of the natural frequency ofoscillation of the crystal itself. The width of the resonance band maybe, for instance 100 kilocycles instead of the usual 2 megacycles.

It will be noticed that in any arrangement of the present inventionthe'waves are not travelling along the cell parallel to the direction ofline scanning as in the case of the device according to British Patentspecification No. 439,236. In that arrangement, owing to the necessityfor the light beam to be parallel in the direction of movement of thewaves, the major restriction of the size of the light source and itsaperture is in the line scanning direction. In the present inventionthere is no restriction in this direction, with consequent increase inlight. The only restriction is in the direction at right angles to this,Where in both cases there is a restriction owing to the necessity offorming a narrow image on the screen, and owing to the necessity forkeeping the width of the low speed scanning member reasonably small. Forexample, the present invention makes it possible to use a cinema arclamp with a large arc crater, and full use of the light available fromwhich such a source can be made.

The piezo-electric crystal assembly may be made from a large number ofsmall crystals stuck on a steel plate, acting as one electrode, andhaving on the other side the separate electrodes for the generation ofthe separate wave-trains. such an assembly acts in a similar way-to thearrangements previously described.

I claim:

l. A television receiver comprising, in combination, a cathode ray tubehaving an electron gun for producing a beam of electrons and anelectrode system for modulating said beam with received picture signalsand with a high frequency electrical oscillation, a light modulatingdevice of the kind utilising the diffraction effeet on light of highfrequency mechanical waves in a liquid medium, said light modulatingdevice comprising a plurality of generators equal in number to thenumber of elemental areas in the picture line for generating a pluralityof parallel trains of high frequency mechanical waves in said liquidmedium, said light modulating device being arranged in the path of saidbeam of electrons so that said beam scans said generators at linefrequency to cause them to produce said trains of waves in said liquidmedium, and an optical system for forming an optical diffraction image01' said trains of waves to reconstitute a picture line on a receivingscreen, and frame scanning means for sweeping said image over saidscreen.

2. A television receiver according to claim 1 wherein said generatorscomprise a piezo-electric crystal assembly having a plurality ofelectrodes arranged on the side thereof remote from said liquid medium aplurality of contacts arranged within said cathode ray tube and in closeproximity to said electrodes, whereby voltages induced on said contactsby said beam of electrons are transmitted to said electrodes by virtueof the capacity existing between said contacts and said electrodes.

3. In combination in a television receiver, means for producing apicture line comprising a supersonic wave light modulating device inwhich there are provided a plurality of generators of mechanical wavesequal in number to the number of elements it is desired to reproduce ina line of the received picture, cathode ray tube commutating means forrelegating to each generator a high frequency oscillation modulated withthat part of the picture signal in each line apportionate thereto, andan optical system for producing from light diffracted by said trains ofwaves a picture line on a screen.

4. A television receiver comprising a light modulating device of thekind utilizing the diffraction effect on light of high frequencymechanical waves in a liquid medium and comprising a plurality ofsimilar generators for generating a plurality of trains of highfrequency mechanical waves in said liquid medium, each traincorresponding to an elemental picture area of a picture line, electronicline-scanning means for exciting said generators one after the otherwith an electron stream modulated in intensity in accordance withreceived picture signals and interrupted at a high frequency suitablefor exciting said generators, optical means for forming an opticaldiifraction image of said trains of waves on a receiving screen, andmechanical frame scanning means for sweeping said image in a directionat right angles to its length over said screen to produce the framescanning component and thus reconstitute a received picture.

5. A television receiver comprising a light modulating device of thekind utilizing the diffraction effect on light of high frequencymechanical waves in a liquid medium and comprising a plurality ofsimilar generators for generating a plurality of trains of highfrequency mechanical waves in said liquid medium, each traincorresponding to an elemental picture area of a picture line, a cathoderay tube having an electron gun for producing a beam of electrons. meansfor modulating said beam with received picture signals and also withhigh frequency suitable for exciting said generators, a plurality ofcontacts, each of said contacts being associated with one of the saidgenerators through an alternating current path, and means for deflectingsaid modulated beam of electrons over said contacts at line frequency,optical means for forming an optical diffraction image of said trains ofwaves on a receiving screen, and me-- chanical frame scanning means forsweeping said image in a direction at right angles to its length oversaid screen to produce the frame mechanical waves in said liquid medium,each v train corresponding to an elemental picture area means forexciting said generators one after the other with an electron streammodulated in intensity in accordance with the received picture signalsand interrupted at a high frequency and optical means for forming anoptical diffraction image of said trains of waves on a receiving screen,said means for exciting said generators comprising a cathode ray tubehaving a first cathode for producing a first electron stream,

means for modulating said stream with the received picture signals andfor deflecting it at line frequency over a plurality of modulatinggrids. a second cathode for producing a second electron stream whichpasses through said modulat' ing grids, a plurality of contacts, meansfor tocussing the electron stream passing through said grids on to saidcontacts, means for modulating said second stream with a highfrequencyoscillation, and means for feeding the voltages produced onsaid contacts to said generators to produce the frame scanning componentand thus reconstitute a received picture.

7. A television receiver according to claim tin which the plurality ofgenerators of said light modulating device are comprised by a singlepiezo-electric crystal extending over the length of the light modulatingdevice and provided with a plurality of electrodes arranged along itslength.

8. A television receiver according to claim 4 wherein the dimension ofsaid modulating device in the direction of movement of the waves whichis the same as the frame scanning direction is such that, in operation,waves representative of more than one line of the received image arepresent therein at anyinstant, and wherein said optical means and saidframe scanning means are adapted to image in the correct position onsaid screen more than one line of the picture simultaneously.

9. In a television receiver, means for reproducing a transmitted pictureline comprising a cathode ray tube, means for modulating the beam ofsaid tube with received picture signals, and with a high frequencyoscillation, a supersonic wave light modulating device having aplurality of identical generators of mechanical waves, equal in numberto the number of elements it is desired to reproduce in a line of thereceived picture, for producing a plurality of trains of waves in saiddevice moving at right angles to the line direction, each traincorresponding to an elemental picture area, a plurality of electrodes insaid cathode ray tube each electrically associated with one of saidgenerators, and means for scanning said electrodes under the influenceof received line scanning oscillations, whereby each generator hasrelegated thereto a high frequency oscillation modulated with that partof the picture signal in each line apportionate thereto, and an opticalsystem for forming on a screen an optical diifraction image of saidtrains of waves to produce the frame scanning component and thusreconstitute a received picture.

FERENC OKOLICSANYI.

